For your soybeans: 15- or 30-inch rows?

Seed costs are high, but so is the cost to knock down weed and insect pests during the growing season. Row spacing goes quite a ways in determining soybean seed cost and in-season treatments. So, what's the right population for your fields?

Narrow row spacing, mostly 15-inch rows, has gained in popularity in recent years because of the likelihood of increased yields. Agriculture Online Crop Talk member JeffO is considering making the switch to 15s. Can this help him attain higher soybean yields? "I've got some information that says 15-inch beans are three to four bushels-per-acre better than 30-inch," he says. "If that's accurate in the real world, I would make the switch. Before I do, give me your real-life examples."

Farmers and fellow Crop Talk members answered JeffO's call. Many say he may find himself using more seed than he wants, or it may be tough to get it done right with his existing equipment that's set up for 30-inch rows. Still, others say they've been able to make the switch without getting new equipment.

Raising soybeans in 15-inch rows does have its advantages. The plants' canopy -- much thicker than with wider rows -- serves several purposes during the growing season, says Iowa State University Extension soybean specialist and High Yield Team member Palle Pedersen.

"Narrow rows have a yield advantage because they achieve canopy closure more quickly and intercept more light throughout the growing season," Pedersen says. "Rapid canopy closure also provides greater shading of weed seedlings as a result of increased light interception by the soybean canopy and can significantly reduce soil moisture loss.

"Canopy closure of 15-inch rows will often happen 15 days earlier than 30-inch rows; this is critical since canopy closure is needed by the start of pod set (R3)," he adds. "Often soybeans grown in 30-inch rows fail to achieve canopy closure by this critical yield-determining growth stage."

A recent one-year trial conducted by Ohio State University Extension in northwestern Ohio shows that 15-inch rows at a seeding rate of 210,000 seeds per acre outyielded 30-inch rows at 185,000 seeds per acre by just over 6 bushels per acre. In the study, the beans were planted in late May and harvested in mid-October. While yields were higher, the difference would have been greater had the beans been sown later, researchers say.

"Past research has shown that narrower-row soybeans typically yield better than wider row spacings," according to a report on the OSU row spacing research. "This yield advantage is even more pronounced with later planting dates. The date (May 31) when it was finally possible to get in the field to plant this trial would be considered a later planting date for this area."

Seed costs are high, but so is the cost to knock down weed and insect pests during the growing season. Row spacing goes quite a ways in determining soybean seed cost and in-season treatments. So, what's the right population for your fields?